Merge pull request #4249 from nlochschmidt/patch-1

Propose kotlinx.serialization as 3rd party lib
diff --git a/kokoro/macos/prepare_build_macos_rc b/kokoro/macos/prepare_build_macos_rc
index dfe66ff..fb97552 100755
--- a/kokoro/macos/prepare_build_macos_rc
+++ b/kokoro/macos/prepare_build_macos_rc
@@ -5,7 +5,7 @@
 ##
 # Select Xcode version
 
-export DEVELOPER_DIR=/Applications/Xcode_8.1.app/Contents/Developer
+export DEVELOPER_DIR=/Applications/Xcode_9.1.app/Contents/Developer
 
 ##
 # Select C/C++ compilers